For all types of substrates, magnetic recording media has begun to incorporate perpendicular magnetic recording (PMR) technology in an effort to increase areal density and is now working toward areal densities of 800 Gbits/in2. Generally, PMR media may be partitioned into two primary functional regions: a soft magnetic underlayer (SUL) and a magnetic recording layer(s) (RL). FIG. 1 illustrates portions of a conventional perpendicular magnetic recording disk drive system having a recording head 101 including a trailing write pole 102 and a leading return (opposing) pole 103 magnetically coupled to the write pole 102. An electrically conductive magnetizing coil 104 surrounds the yoke of the write pole 102. The bottom of the opposing pole 103 has a surface area greatly exceeding the surface area of the tip of the write pole 102. As the magnetic recording disk 105 is rotated past the recording head 101, current is passed through the coil 104 to create magnetic flux within the write pole 102. The magnetic flux passes from the write pole 102, through the disk 105, and across to the opposing pole 103 to record in the PMR layer 150. The SUL 110 enables the magnetic flux from the trailing write pole 102 to return to the leading opposing pole 103 with low impedance.
Typically, higher areal densities are typically achieved with well-isolated smaller grains in the PMR layer. A higher magnetocrystalline anisotropy constant (Ku) is typically required to resist the demagnetization effects of the perpendicular geometry and to keep the smaller grains thermally stable to reduce media noise. For example, smaller grain size (<7 nm) and high magnetocrystalline anisotropy (Ku) L10 ordered FePt media can achieve areal density beyond 1 Tb/in2 magnetic recording.
With the advent of heat-assisted magnetic recording (HAMR) media, areal densities of 900 Gbits/in2 and higher using PMR technology has been realized. This is because HAMR media comprises of a magnetic compound, such as a FePT alloy, that has a higher magnetic stability than PMR technology using non-HAMR media. However, because the HAMR media comprises of such higher-stability magnetic compounds, HAMR media requires that heat be applied to it before changes its magnetic orientation can be changed. Typically, when PMR technology magnetically records data to HAMR media, it first uses a heating element, such as a laser, to increase the temperature of the recording location on the media, in order to lower the location's high magnetic anisotropy constant (Ku) sufficiently to allow a change to its magnetic orientation (i.e., record data).
FIG. 2 illustrates a cross-sectional view of an exemplary heat-assisted magnetic recording (HAMR) media comprising a hard magnetic recording layer 206, a soft magnetic underlayer (SUL) 210, a heatsink layer and non-magnetic interlayer 208 between the hard magnetic recording layer 206 and soft magnetic underlayer 210, and a bottom substrate 212. The hard magnetic recording layer 206 illustrated is a L10 layer made of iron platinum (FePt), a magnetic compound known to have a high magnetic anisotropy constant (Ku). Other suitable compounds for the hard magnetic layer include iron platinum alloys (FePtX), such as FePtCu, FePtAu, FePtAg, and FePtNi.
Disposed over the hard magnetic recording layer 206 are a capping layer, an overcoat 204, and a lubricant 202. The overcoat 204 is formed to meet tribological requirements such as contact-start-stop (CSS) performance and corrosion protection. Materials usually utilized for the overcoat layer 204 include carbon-based materials, such as hydrogenated or nitrogenated carbon. A lubricant 202 is placed over the overcoat layer 204 to further improve tribological performance. Exemplary lubricants include a perfluoropolyether or phosphazene lubricant or a composite thereof.
It has been discovered that certain dopants/segregation materials, such as carbon (resulting in FePtX:C), when added to a FePt-alloy of a hard magnetic recording layer results in small grain size, granular microstructure, high magnetocrystalline anisotropy (Ku), high coercivity (Hc), good texture and ordering, and lower ordering temperature, all of which are desirable properties for HAMR media. For example, adding 30-40% C to FePt (grown directly on an interlayer comprising MgO) gives provides a magnetic recording layer having a grain size (6-8 nm) and a lower L10 ordering (deposition) temperature.
It has been discovered that by using small grain size <7 nm and high magnetocrystalline anisotropy (Ku) L10 ordered FePt media, areal densities beyond 1 Tbits/in2 can be achieved magnetic recording. It has also been discovered that the formation of small grain size, good texture, high coercivity (Hc), high anisotropy constant (Ku), narrow switching field distribution, low media roughness, high thermal conductivity, and good corrosion in low dopant content hard magnetic layer (e.g., FePt:C; or FePt:oxide) can be induced by utilizing a proper interlayer. For example, to achieve high coercivity (Hc), granular structure and small grain size FePt hard magnetic recording layer, MgO thin film has typically been used as an interlayer grown on top of the amorphous seed layers, heatsink layer and soft magnetic underlayer (SUL).
Unfortunately, MgO suffers from some drawbacks such as low deposition rate (˜1-2 Å/kW·s), low thermal conductivity, poor corrosion properties, large grain size (˜8-20 nm), and large Δθ50 characteristics (i.e., FWHM is >15°) causing large c-axis dispersion of ordered FePt film.